The present invention relates to a drill bit for drilling and, in particular, rotary percussion drilling a hole and, in particular, a tap hole of a blast furnace, wherein the drill bit is comprised of a drill head including a plurality of hard-material or hard-metal inserts and a base body to be connected with a driving element or the like for actuating or powering the drill bit, said hard-material or hard-metal inserts being received in bores or openings of the drill head, wherein at least one hard-material or hard-metal insert, on its end received within the drill head, is at least partially designed with a curved or cambered surface contour that cooperates with a complementary, cambered or curved surface of the drill head and/or the base body.
In the context of drill bits or crowns it is known in order to increase the drilling performance, to fix a plurality of hard-material or hard-metal inserts in a head, whereby such fixing can, for instance, be realized by using sleeve-shaped inserts as can be taken, for instance, from EP-B 0 581 534, U.S. Pat. No. 4,951,672, EP-A 0 573 135, EP-A 0 943 780 or EP-A 0 353 214. Moreover, it is known to solder such hard-material or hard-metal inserts to, for instance, the base material of a drill head in order to avoid falling out of said hard-material inserts as can be taken, for instance, from DE-A 34 08 225. Known hard-material or hard-metal inserts in the context of the production of a drill bit usually comprise, on the cutting part projecting out of the drill head, a plane extending substantially normal to the longitudinal axis of the insert and possibly resting on an accordingly plane surface of the base material for the purpose of force transmission, while, according to DE-A 34 08 225, a recess is provided below the ends of the inserts such that no direct contact is provided between the insert and the bore. Bearing in mind the rough operating conditions and the forces to be applied particularly in rotary percussion drilling, and due to the usually not completely uniform load exerted on the drill bit and, in particular, the hard-material or hard-metal inserts, which are partially arranged at an angle relative to the longitudinal axis of the drill bit so as to cover an appropriate drilling surface, eccentric or nonuniform stresses occur on the hard-material inserts such that no proper force transmission from the drill head or base material to the hard-material or hard-metal inserts will be readily ensured, in particular with a progressive operating time on account of wear.
An embodiment of the type mentioned above can for example be taken from U.S. Pat. No. 5,558,170, wherein receiving openings for the hard-material or hard-metal inserts have to be formed with a special tool.
The present invention aims to ensure, with hard-material or hard-metal inserts being provided or arranged on the drill head of a drill bit, that even in the event of a nonuniform stress or wear of such hard-material or hard-metal inserts an accordingly large area or large and substantially constant surface region will be provided for the transmission of the impact energy required to obtain an accordingly rapid drilling progress and to prevent that an insert being potentially loosened falls out.